Photographic sound-recording apparatus



April 14, 1931. I A. TAYLOR 1,801,123

PHOTOGRAPHIC SOUND RECORDING APPARATUS Filed Jan. 51, 1930 Inventor Laur'ens A.Tagl.or, b5 60k.

HLs Attorne g.

Patented Apr. 14, 1931 v UNITED STATES PATENT OFFICE LAURENS A, TAYLOR, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK PHOTOGRAPHIC SOUND-RECORDING APPARATUS Application filed January 31, 1930. Serial No. 424,993.

My invention relates to apparatus forcurrents; Various well known constructions photographically recording sound on a moving light sensitive member. More particu- .larly it relates to sound recording apparatus of the form in which the film is exposed by the projection thereon of a narrow transverse band of light which is varied'in accordance with the sound waves. It is well known to those skilled in the sound recording art that the upper limit of Wave frequency which may be recorded faithfully with such apparatus depends upon the width of the light band and the speed at which the film is moved past the light band. While excellent results have been obtained with commercial positive film stock moved during both recording and reproduction at a speed of ap roximately ,90 feet per minute past a light and of the order of one one-thousandth of an inch in width, there is nevertheless an appreciable loss in the high frequencies of the sound due to the fact that the ratio of the width of the light band to the wave lengths of those high frequencies is too-high.

One obj eet of my invention is the provision of improved sound recording apparatus which shall automatically compensate for such losses in the high frequencies. Another object of my invention isthe provision of recording apparatus having improved means for monitoring the recording process which is unaffected by suchcompensation.

My invention will be better understood from the following. description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the single figure of the drawing which illustrates diagrammatically one embodiment of my invention I have shown at 1 a suitable sound pick-up device, for example, a condenser microphone, connected by the wires 2 to a suitable recording amplifier 3 which preferably is of the well known thermionic type. In the circuit connections 4 between the amplifier 3 and the means, to be described later, for varying the film' exposing light is the compensator 5 whose function it is to produce in effect an increased amplification of the higher frequencies of the sound wave capacity 7, the values of which are chosen to may be employed for the compensator. For example, I have shown it as a frequency responsive variable impedancecomprising the non-inductive resistance 6 shunted by the produce a rising frequency-amplitude characteristic of the desired form and value.

The sound is recorded on the film 9 and the record may be made in accordance with either the variable density method or the variable width method. 'I have chosen to illustrate my invention as comprising apparatus for making a record of the variable width type and for this purpose I have shown the light source 10 from which light is concentrated by the lens 11 on the mirror 12 of an oscillograph 'galvanometer, of which only the moving element 13 is shown, the same being connected by the wires 4' to the compensator 5. 70

The light beam reflected by the mirror 12 of the galvanometer passes through a suitable optical system by means of which the reflected beam is focused in the narrow transverse band 14 on the film. The optical system illustrated is of well known construction and may be briefly described as comprising the cylindrical lens 15, lens 16, apertured stop 17 and objective 18. With the apparatus described above it will be seen that compensation may be made for the loss of the higher frequencies incident to the ratio of the width of the light band 14 to the wave length. Moreover, compensation may be made not only for high frequency losse s sustained during recording but also for high frequency losses occurring for the same reason during reproduction.

In order that the operator of the recorder at all times during the recording process may know exactly how the apparatus is operating, the recorder commonly is provided with some form of monitoring apparatus. With a variable width recorder, such as I have illustrated, I have employed for this purpose the 95 apparatus shown on the drawing which comprises the small mirror 19 arranged to reflect throu h the apertured screen 20 and lens 21 into t e photo-electric cell 22 a part of the light beam vibrated by the galvanometer mir- 100 ror 12. This apparatus is described and claimed in m copending application Serial No. 424,992, led Jan. 31, 1930. The output of the photo-electric cell 22 after being amplified in the usual manner, such for example,

as the thermionic amplifiers 23 and 24 is fed to a suitable sound producer which in the present case is shown as the monitoring loud speaker 25. Inasmuch as the vibrations of the galvanometer mirror are subject to the modifying efiect of the compensator 5, the

tric cell 22 in a manner to produce the opposite efi'ect of that of the compensator 5. For this purpose I have provided the second compensator 27 This may be of any well known construction provided it produces a drooping frequency-amplitude characteristic. I have shown, for example, a frequency responsive variable impedance shunt comprising the resistance 28 andcapacity 29 connected in series across the monitoring circuit between the amplifiers 23 and 24, the values of the resistance and capacity being such as to give a characteristic of the desired form and value to neutralize the effect of compensator 5. Thus with this monitoring apparatus the sound heard by the operator may be made to correspond very closely, if not exactly, with that which would be heard upon reproduction of the film record. It will be understood that the particular forms of the compensators shown are merely illustrative of various well known constructionswhich may be employed for that purpose. .For example, under certain conditions I may employ for the compensator 5 a frequency responsive variable impedance shunt of well known form having a portion tuned to the higher frequency, say 5000 cycles. I may also effect the desired compensation for recording by a special construction of the galvanometer, thereby making a separate compensator element unnecessary.

I have chosen the particular embodiment described above as illustrative only of my invention and it will be apparent that various modifications may be made without departing from the spirit and scope of my invention which modifications I aim to cover by the appended claims.

lVhat I claim asnew and desire to secure by Letters Patent of the United States is:

1. Apparatus for recording sound on a moving light sensitive member and for monitoring said recording comprising means arranged to variably expose the light sensitive member in a narrow transverse area in accordancewith the sound waves, said means emmas being constructed to respond to a relatively greater degree to the higher frequencies of the sound waves than to the lower frequencies thereof, a sound producer, and operating means therefor responsive to said exposing means and constructed to produce a smaller response to the higher frequencies than to the lower frequencies.

2. Apparatus for recording sound on a moving light sensitive member and for monitoring said recording comprising light varying means responsive to the sound waves arranged to expose the light sensitive member in a narrow transverse area, means for causing a relatively greater response of said light varying means to the higher frequencies of the sound than to the lower frequencies thereof, a sound producer operated by said light varying means, and means operative to cause a'smaller response by said sound producer tothe higher frequencies than to the lower frequencies.-

3. Apparatus for recording sound on a moving film and for monitoring the record-v ing process comprising a sound pick-up device, means connected therewith for illuminating a narrow transverse area of said film, means in said connection for effecting a relatively greater response of said illuminating means to the higher frequencies of the sound than to the lower frequencies thereof, a sound producer, a photo-electric device connected therewith and arranged to be actuated by said illuminating means, and means for .efiecting a smaller response of said sound producer to the photo-electric device at said higher frequencies than at the lower frequencies.

4. Apparatus for recording sound on a moving film and for monitoring the recording process comprising a sound pick-up device, a source of light, a galvanometer connected with said pick-up device and arranged to vibrate a narrow band of light from said source on the film, compensating means in the connectionbetween the pick-up device and the galvanometer constructed to cause a relatively greater amplitude of vibration of the light band for the higher frequencies, a loud speaker, a photoelectric cell arranged to be actuated by said light vibrations, and a second compensator connected with said cell and loud speaker and constructed to produce a relatively smaller amplitude of the higher frequencies of the emitted sound.

In witness whereof, I have hereunto set my hand this 30th day of January, 1930;

' LAURENS A. TAYLOR. 

